Abstract Adipose tissue plays a central role in metabolic and energy homeostasis, and dysregulation of adipocyte function is fundamental to the pathogenesis of the metabolic syndrome. Our group has a track record of identifying and characterizing important proteins involved in adipocyte biology, including PPAR?, TLE3, and PSPC1. Recently, we uncovered a novel physiological regulator of adipose thermogenic activity: the cytokine IL10. This proposal builds upon this discovery to address important questions regarding the regulation of systemic metabolism, adipose thermogenesis, and the crosstalk between immune cells and adipocytes within adipose tissue depots. Regulatory pathways that stimulate adipose tissue thermogenesis have been extensively characterized, but the limiters of energy expenditure have remained poorly defined. We have discovered that IL10 signaling through STAT3 in adipocytes regulates thermogenic gene expression and energy expenditure. The IL10 receptor alpha (IL10R?) is highly enriched in mature adipocytes and is induced in response to differentiation, obesity, and aging. Preliminary data indicate that IL-10 signaling inhibits beta- adrenergic signaling in beige adipocytes, and reduces the occupancy of ATF and C/EBP? on thermogenic gene promoters. Moreover, inhibiting the expression of the IL10 receptor alpha (IL10R?) in adipose tissue with antisense oligonucleotides (ASOs) is protective against diet-induced obesity, suggesting that the adipose IL10 axis might be targeted therapeutically. Here we propose to further define the specific cell types and tissues that produce and receive IL-10 signals affecting metabolism, to elucidate the mechanisms by which IL10 signaling regulates adipocyte gene expression, and to understand the roles of adipose tissue immune cell populations in the regulation of thermogenesis by IL10. Specific Aim 1 is to characterize the adipocyte-intrinsic role of IL-10 signaling in lipid storage and thermogenesis in adipose tissue. Specific Aim 2 is to define the mechanisms underlying transcriptional modulation of thermogenesis by IL-10. Specific Aim 3 is to delineate the role of adipose tissue-resident immune cells in the regulation of thermogenesis by IL10.